For all groups In the recovery room after surgery, boluses of 2mg intravenous morphine will be given every 5 minutes until numerical rating pain score (NRS) is less than 4/10. A PCA machine will then be connected. The machine will be configured to give 1mg of morphine at a time and the lockout duration will be set to 5 minutes. No background infusion will be given and the maximum dose limit will be 0.1mg/kg per hour of morphine sulphate.